Bitcoin Bridge

A Bitcoin bridge is any mechanism for moving BTC's value onto another blockchain so it can be used in that chain's applications. The bridge holds the real BTC (or claims to) and issues a representation - a "wrapped" version - on the destination chain.

Major patterns:

• Custodial wrapped BTC. WBTC on Ethereum is the canonical example: a custodian holds real BTC and issues ERC-20 tokens 1:1. BitGo held the reserves on its own until 2024, when custody moved to a joint venture of BitGo and BiT Global that spreads the keys across several jurisdictions. Users trust that custodian.
• Federated bridges. Liquid Network keeps pegged BTC in an 11-of-15 multisig whose keys are held by 15 functionaries run by members of its federation. Rootstock (RSK) began with a federation and later moved to its PowPeg, where the multisig keys sit in hardware modules that sign only when Rootstock's proof-of-work chain commands it. Less trust-minimized than non-custodial but more decentralized than a single custodian.
• Threshold-signer bridges (tBTC, sBTC). Spread custody across a group of signers using threshold signatures. tBTC uses a randomly selected group of operators and needs a majority of them to act; sBTC needs 70% of its signer set to approve any spend.
• Atomic swaps. Not technically a bridge - direct peer-to-peer exchange where BTC stays on Bitcoin and the counterparty asset stays on its native chain. No wrapped token involved, no trust required, but requires a counterparty willing to swap.

The track record is grim. Chainalysis estimated in August 2022 that $2 billion had been stolen in 13 cross-chain bridge hacks, most of it that year. Big ones included Ronin Bridge (almost $600M, March 2022), Wormhole ($323M, February 2022), Nomad Bridge ($190M, August 2022), Harmony Horizon (nearly $100M, June 2022), and many smaller incidents. Bridges are among the most-targeted attack surfaces in the broader crypto landscape because they're high-value honeypots holding pools of locked assets. Bitcoin's own federated pegs are not immune: in September 2026 a software bug let an attacker take about 3,996 BTC out of Liquid's peg, and 3,400 BTC was later returned (see Liquid Network).

The Bitcoin-only perspective: bridging BTC to other chains exposes it to those chains' risks, regulatory profiles, and smart-contract bug surfaces - all things Bitcoin was designed to avoid. The honest framing is that bridges trade Bitcoin's security properties for access to other ecosystems' applications, and historically that trade has been expensive.

If you genuinely need BTC value on another chain (for arbitrage, specific DeFi exposure, whatever), accept the custodial / smart-contract risk knowingly. For everything else, keeping BTC on Bitcoin itself, on-chain or over Lightning, avoids that extra layer of risk.